The present invention relates generally to computerized image processing, and more specifically to techniques for determining whether an image is substantially blank.
One context that presents some unique challenges to computerized image processing is a form that has been faxed. Consider a scenario where a user instructs a computer to perform jobs based on marks (typically made by hand) in various mark-sense fields on a form. The system is intended to be used remotely, with the user sending the form by fax to a fax modem in the computer. In the event that the user does not have a form, a suitable protocol is for the user to fax a blank page (or a page with a large slash or X) to the computer. The computer would interpret this as a request for a starter form that could be used to request other forms.
What the computer gets, however, is likely to be somewhat removed from a blank image. The image may contain text written across the top of the page by the sending fax, pepper noise (isolated black pixels in white regions, or vice versa), and thin horizontal lines of black pixels in white regions, or vice versa, due to noise on the telephone line. The image is further subject to scanner noise which can manifest itself as vertical black streaks due to opaque material on the scanning platen of the fax machine. For the blank page to be interpreted as such, the computer must be able to distinguish the noise from possible intended information on a form. Additionally, it must do this quickly, since it must perform this screening on every single-page input image. Furthermore, it must do this with finesse, since it would be undesirable to have starter forms sent out in response to input of legitimate content-bearing forms.